The present invention relates to a method of removing a metal, in particular a heavy metal, from a stream of hot gas, wherein a particulate material comprising calcium and aluminum-silicate is contacted with the hot gas containing metal in the gaseous phase, which particulate material adsorbs the metal.
Such a method is known in the art, for example for the cleansing of flue gas released during the combustion of coal. A mixture of calcium hydroxide particles and kaolin (an aluminum silicate) particles is introduced in the hot flue gas to adsorb a metal present, such as lead or nickel. The mixture is a physical mixture. Special care is taken to use particles as small as possible. High-grade kaolin, characterized by its small particle size, is used to obtain optimum performance. Kaolin is the compound actually adsorbing the metal. The function of calcium hydroxide is to scavenge negatively charged ions such as sulfate and chloride, which have an adverse effect on the performance of the kaolin.
This method has several disadvantages. Firstly, the starting materials, and in particular kaolin, are expensive. Furthermore, virgin kaolin is a finite natural resource. Secondly, extremely fine grinding and/or the use of precipitation techniques adds to the cost.
The object of the present invention is to alleviate the above mentioned disadvantages.